The endocrinology of reproduction in lampreys and applications for male lamprey sterilization

This review briefly summarizes the latest findings on the reproductive endocrinology of sea lampreys (Petromyzon marinus) and the application of these findings to the control of sea lamprey populations by sterilization. Since the last Sea Lamprey International Symposium (SLIS) meeting in 1979, substantial new evidence has now clearly shown that lamprey reproduction is controlled by the neuroendocrine axis. This evidence includes the identification of reproductive hormones-five brain and six pituitary hormones of lampreys have been identified between 1986 and 2000. In addition, there have been extensive physiological and immunological studies on lamprey reproduction. It is concluded that lamprey reproduction is a highly synchronized process that is initiated and mediated by a complex neuroendocrine coordination and integration of environmental cues and hormonal mechanisms. This newly acquired information permits the pursuit of a new approach of sterilization for control of reproduction in male lampreys. It is proposed that lamprey gonadotropin-releasing hormone (GnRH) analogs can be developed for sterilizing sea lampreys in a sterile-male-release program in the Great Lakes region. This approach could complement other methods being used to control sea lampreys. The potential of using GnRH analogs (antagonist) is high because these compounds are proteins which are easily degraded within the organism, are non-toxic to humans, are easy to administer, can be administered in the field, are low in cost, and are relatively easy to synthesize. This report includes a summary of the experiments to identify putative GnRH agonists/antagonists that inhibit spermatogenesis without destroying the mating competitiveness of males.